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Article

Photocatalytic Remediation of Carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs) Using UV/FeCl3 in Industrial Soil

by
Mohamed Hamza EL-Saeid
*,
Abdulaziz G. Alghamdi
,
Zafer Alasmary
and
Thawab M. Al-Bugami
Department of Soil Sciences, College of Food and Agriculture Sciences, King Saud University, Riyadh 11451, Saudi Arabia
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(10), 956; https://doi.org/10.3390/catal15100956
Submission received: 7 September 2025 / Revised: 28 September 2025 / Accepted: 1 October 2025 / Published: 5 October 2025
(This article belongs to the Special Issue Advances in Photocatalytic Wastewater Purification, 2nd Edition)
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Abstract

Currently, the potential environmental concerns around the world for polycyclic aromatic hydrocarbon carcinogenic (PAHCs) contamination as carcinogenic compounds in industrial soils (automobile industry) are rising day by day. At present, the technology of treating contaminated soils using photocatalysts is commonly used; however, this study tested photolysis and photocatalysis through ultraviolet light (306 nm) due to its high treatment efficiency. FeCl3 (0.3, 0.4 M) was used as an iron catalyst for each treatment in the presence of H2O2 (10%, 20%) as an oxidizing agent. The impact of light treatment on soils that contained various concentrations of PAHCs like naphthalene (NAP), chrysene (CRY), benzo(a) pyrene (BaP), indeno (1,2,3-cd) pyrene (IND) was investigated. The QuEChERS method was used to extract PAHCs, and a gas chromatograph mass spectrometer (GCMSMS) was used to determine concentration. The concentrations of PAHCs were measured for soils at intervals of every 2 h after exposure to ultraviolet rays. The results showed a decrease in PAHCs concentrations with increased exposure to UV irradiation, as the initial values were 26.8 ng/g (NAP), 97 ng/g (CRY), 9.1 ng/g (BaP) and 9.7 ng/g (IND), which decreased to 2.17 ng/g (NAP), 3.14 ng/g (CRY), 0.33 ng/g (BaP) and 0.46 ng/g (IND) at 20, 40, 30 and 40 h of UV exposure; moreover, with an increase in concentration of the catalyst (0.4 M FeCl3 with 20% H2O2), NAP, CRY, BaP and IND became undetectable at 8, 26, 14 and 20 h, respectively. It was concluded that a significant effect of ultraviolet rays on the photolysis of PAHCs, along with Photovoltaic at 306 nm wavelength, was observed while using FeCl3 (0.4 M) combined with H2O2 (20%) produced better results in a shorter time compared to FeCl3 (0.3 M) with H2O2 (10%).

Graphical Abstract

1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) are chemical compounds that contain benzene rings ranging from two in numbers to as many, which are carcinogenic and are classified as persistent organic pollutants (POPs). They act as a source of carcinogenic (PAHCs), mental illness and heart disease [1].
PAHs have a variety of sources and many risks are associated with them, including those related to the environment and natural processes. Major sources include emissions from combustion processes in forest fires, oil spills and volcanic eruptions, human activities like combustion or pyrolysis of biomass, burning of fossil fuels or products derived from fossil fuels like coal, oil, gas, coal tar, vehicle emissions and soil waste combustion [2].
Therefore, it is necessary to treat contaminated soils using modern yet inexpensive methods that do not cause health or environmental damage. There are many techniques for treating PAHs in contaminated industrial soils, and most of these work on advanced oxidative processes (AOPs). Such decontaminating methods help to determine pollutants concentration, time of residence in the soil environment and their distribution ratios [3]. Photocatalysis is an emerging method for degrading PAHs in soils [4]. The sunlight is composed of three components, namely visible light (400–700 nm), UVA light (320–400 nm) and UVB light (280–320 nm), and among them, visible light and UVA have the best results on the degradation of PAHs [5].
Recently, a significant advancement in the use of semiconductor photocatalysis has been observed [6]. Heterogeneous semiconductor photocatalysis is a cost-effective and extensively utilized method for the degradation of organic pollutants [7]. Semiconductor-based photocatalysis is popular due to its environmental applicability and creating renewable energy sources, and demonstrates a clean-up process [8]. In addition, heterogeneous photocatalysis is an integral part of advanced oxidation processes (AOPs) and has great potential for degrading pollutants [9]. In this regard, Jia et al. [10] reported the photocatalytic dehydrogenation of ethanol using TiO2. Valenzuela et al. [11] stated in their review that organic transformations can be carried out by employing oxidation and reduction reactions, isomerization reactions, C-H bond activations and C-C and C-N bond-forming reactions. Bastani et al. [12] highlighted the importance of unconversion nanoparticles (UCNPs) in pollution degradation. Photo mineralization of polycarboxylic benzoic acid was observed in UV irradiation aqueous suspension [13].
Photocatalytic activities of CuOx/TiO2 were evaluated by photodegradation of organic pollutants under visible light illumination. The prepared CuOx/TiO2 composites exhibited a unique structure, in which CuOx clusters with about 2–3 nm nanocrystals were uniformly distributed on the TiO2 and improved its photocatalytic activity, promoting the practical application of the TiO2 photocatalyst [14].
Many of the semiconductor metal oxides are utilized in the photocatalysis of PAHs. For example, ZnO has a wide band gap of approximately 3.37 eV, due to which it is only receptive to the UV region of the spectrum. Scientists have altered ZnO with non-metal elements, which effectively narrowed its band gap [15]. TiO2 is a low-cost, more chemically stable material that does not require reagents [16]. Certain modification strategies are being implemented for enhancing the efficacy of metal oxide nanoparticles, enabling utilization in daylight. The modification processes include adding elemental or oxide states on their surface or within the texture. Such modifications create a band gap energy due to changes in the electronic arrangement of assembled compounds [17].
However, research has been particularly centered on the use of TiO2 due to its positive attributes like abundance, stability and nontoxic nature [18]. But also, TiO2 has a high band gap of 3.2 eV, which causes hindrance in its efficacy [19]. The fabrication of nano composites by using graphene oxide, carbon nanotubes, semiconductors and metal–organic frameworks augments the efficacy of TiO2 [20,21]. Carbon-based nano composites, due to their electrical mobility and higher specific area, create plasmonic and Schottky effects [22,23]. Halloysite-based nano composites are also used for the photodegradation of organic pollutants [24]. Phyllosilicate minerals like rectorite, kaolinite and montmorillonite also improved the photocatalytic activity of MoS2, ZnO, gC3N4 and TiO2 [25]. Research has also been carried out on the surface modification of the most typical photocatalyst (TiO2). Adding nanoparticles like Au, Ag, Pd and Pt functions as electron traps and rapid electron migration takes place from the photocatalyst to metal nanoparticles due to the formation of a Schottky barrier at the interface. Noble metals also have surface plasma resonance properties, which promote excitation of photocatalysts under visible light facilitating interfacial electron transfer [26]. Plasmonic effects occur due to the presence of metallic nanostructures, which enhance the efficacy of the catalyst by creating oscillation of conduction electrons which helps to augment electron transport [27]; however TiO2-based semiconductors mostly work on dielectric MIE resonances [28]. Heterostructures like plasmonic photocatalysts are popular in photocatalytic systems. Plasmonic catalysts include noble metals, conducting oxides and metal-based nanostructures. These nanostructures have wider applicability in Fischer–Tropsch synthesis (FTS), dry reforming of methane (DRM), reverse water gas shift (RWGS) and CO2 hydrogenation [29,30].
The Fenton reaction is one of the effective and environmentally friendly options for degrading organic pollutants. Photocatalysis in this process, however, works when they receive UV light energy of the required wavelength. Research shows that 306 nm wavelength results in Fe3+ complex’s reduction to Fe2+ and can effectively occur at λ ≥ 380 nm in photocatalysis and photo-Fenton systems [31]. In the photo, Fenton reactions, solar and ultraviolet irradiations are widely used. Sunlight is cost-effective but requires large areas for exposure and results in low control over the radiation provided in the process.
UV irradiation consists of high-energy photons that absorb PAHs directly. Apart from using UV irradiation with catalysts, natural photodegradation also takes place. This process involves both direct and indirect photolysis. Other sources that are effective in PAHs photolysis are visible light. It works on the specific catalyst. Like modified carbon nitride combined with TiO2.
Conventional UV mercury lamps have a high operational cost and consume higher electricity [32]. LED lamps are an alternative in the photo-Fenton process, and various studies have implemented their use for the degradation of organic pollutants [33]. Visible LED lamps have potential in this field as they are cost-effective, have lower electricity consumption, high photon efficiency and the possibility of emission at selective or wider wavelengths [34].
There have been remarkable developments in the field of photocatalysis; however, apart from hot charge carriers under UV light, plasma-driven routes are also under debate as localized surface plasmon resonance (LSPR) degenerates and produces excited charge carriers and retains higher energy in comparison to charge carriers that are directly photoexcited [35]. Processes like photo thermal reactions use light and heat as an energy source, enabling efficient solar energy trapping in the light spectrum. As a result, the visible and infrared photons are also covered, which in other processes are inadequate to excite photocatalytic processes [36,37,38].
Previous studies have revealed that a temperature rise can quantitatively reduce the toxicity of metal-contaminated soil. However, this research was effective for static pollutants and followed coupled adsorption. On the other hand, the actual transport of pollutants in the soil is temperature-dependent and follows dynamic pathways; in this regard, a thermos-hydro-mechanical two-phase flow coupling transportation model was fabricated and showed positive results-based temperature-driven effects [39]. Graphite carbon nitrite is popular due to its high visible light response [40]. Bi2O3 is another cost-effective crystal that is widely used in catalysis. The α-Bi2O3 and β-Bi2O3 can be activated under visible light wavelength but its recombination photoinduced electron hole limits its practical implication [41].
The creation of hydroxyl radicals (OH) leads to a variety of distinct chemical reactions. The extremely reactive nature of OH radicals make them ideal for attacking a variety of chemical molecules. Using photocatalytic decomposition of PAHs with UV light under iron catalyst (FeCl3), this reaction is known as a Fenton-like reaction [42].
H2O2 + Fe+ → Fe 3+ + OH• + OH−
In the photo-Fenton reaction, which takes place under the influence of UV radiation, the Fe2+ ions are regenerated along with an additional OH radical, which is not the case with the basic Fenton reaction (without UV radiation). Moreover, the photo-Fenton reaction reduces more Fe3+ to Fe2+ and more OH radicals (Equation (2)). Under this process, an increased efficiency in pollutant degradation is observed. This photo-Fenton reaction also causes the formation of hydroxyl radicals under light influence (Equation (3)).
Fe3+ + H2O + λυ → Fe2+ + OH• + H+
H2O2 + λυ (UV) → 2HO
The radicals produced as end product have the capability to mineralize wide range of organic pollutants. But there are studies which affirm that soil characteristics like hydrophobicity (which is due to the presence of organic matter), structural complexity and low solubility, which hinders the degradation of certain pollutants [43,44].
In another study, it was stated that heterogeneous photo-Fenton-like process was more effective in removing azo dye in comparison with the heterogeneous Fenton-like process by giving 94.71% decolorization activity [45]. Figure 1 shows the decomposition of organic compounds through the Fenton process.
The process of photo-Fenton with FeCl3 as an accelerator showed 51.5%, 63.2% removal percentages for TN and TOC > 90% of a separation percent of >90% for turbidity, TP and TOC [46]. Pretreatment with Fenton’s reagent and an aerobic biological procedure Fenton reagent-biologic combined technique, enabled elimination of 80.7% COD and 93.7% TP globally at a pH of 3.5, 0.20 H2O2/COD ratio and 15 H2O2/Fe2+ molar ratio [47]. Nieto et al. [48] and Hodaifa et al. [49] carried out a study in which the reaction was catalyzed by FeCl3 and the Fenton reagent. Both researchers used a comparable ratio of (FeCl3/H2O2) to achieve COD reduction exceeding 90%. The study by Hodaifa et al. [46] showed that the optimum balance was between 0.026 and 0.058 w/w, while Nieto et al. [48] presented the optimum ratio value of 0.04. García and Hodaifa [50] employed a medium-pressure of UV lamp and FeCl3 as a catalyst in photo-Fenton oxidation. Over 95% of the total organic carbon (TOC) and COD elimination and a (FeCl3/H2O2) ratio of 0.125 was attained. A photo-Fenton method using fictitious sun radiation was employed and TOC removal was up to 95%. There was a Fenton-like reaction in which the catalyst FeCl3 in the presence of hydrogen peroxide gave 95% degradation efficiency of organic matter and phenolic compounds in olive-oil mill wastewater (OMW) [48].
Scientists have revealed that photocatalytic degradation was accelerated in acidic/alkaline conditions compared to neutral soil conditions [51]. Similarly microbial activities and chemical reactions also impact the degradation rate for bound residues of polycyclic aromatic hydrocarbons, hence prior to UV exposure, such factors need to be kept in mind; [52,53] stated that photodegradation of PAHs decreased with the increase in soil depth; moreover, benzo[a] pyrene and pyrene degradation was influenced by soil particle sizes (1 mm soil showed fastest degradation rate).
In this experiment, the removal of naphthalene (NAP), chrysene (CRY), benzo (a) pyrene (BaP) and indeno (1,2,3-cd) pyrene (IND) pollution from industrial soils in Riyadh, Saudi Arabia, where the source of pollution for industrial soils is automobiles, was assessed. This experiment will determine the application efficiency of FeCl3/H2O2 treatments on the above-mentioned pollutants. Due to the toxicity, numerous risks and ongoing pollution of industrial soil regions by these compounds, contaminated soils were treated in this work by using iron catalysts and UV light at a wavelength of 306 nm, as well as oxidizing agents. This research will help develop a low-cost and high-impact method to combat the carcinogenic polycyclic aromatic hydrocarbons (PAHs) pollution.

2. Results

The results revealed that mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) at wavelength 306 nm in Control treatment (without Photochemical treatments), the PAHCs concentrations slowly decreased with time. The degradation was accelerated when our samples were exposed to UV 306 nm wavelengths for 2 h as shown in Table 1 and Figure 2. The values were 24.66, 95.11, 8.91 and 9.06 for NAP, CRY, BaP and IND, respectively. Similarly, when the exposure was made for 20 h at UV 306 nm wavelengths, the concentration decreased to 2.17, 54.46, 2.27 and 3.77 for NAP, CRY, BaP and IND, respectively. However, their concentration was detectable at 22 h for NAP, 42 h for CRY, 32 h for BaP and 42 h for IND. The addition of catalytic treatments (FeCl3) and oxidizing agent (H2O2) at different percentages under UV 306 nm exposure also affected the concentration of specific carcinogenic PAHCs in the soil samples under study. The highest reduction rate of carcinogenic PAHCs was observed in the 0.4 M FeCl3 with 20% H2O2 followed by the 0.3 M FeCl3 with 10% H2O2-treated soil. In case of 0.3 M FeCl3 with 10%H2O2 a decrease in the concentration PAHCs was observed with increasing exposure time, as shown in Table 2 and Figure 3. The pollutants exposed to 2 h at UV 306 nm wavelengths gave values of 22.11, 93.55, 8.69 and 9.04 for NAP, CRY, BaP and IND, respectively. When the exposure time was 10 h. the concentration decreased to 4.66, 70.19, 3.66 and 4.07 for NAP, CRY, BaP and IND, respectively. However, the concentration was not detected at 12 h for NAP, 32 h for CRY, 22 h for BaP and 26 h for IND. PAHCs at 0 h (control) gave concentrations as 26.8, 97.7, 9.1 and 9.7 ng/g for NAP, CRY, BaP and IND, respectively.
Our results showed that the maximum degradation of PAHCs was observed at UV (306 nm), 0.4 M FeCl3 with 20% H2O2-treated soil. A decrease in the concentration of carcinogenic PAHCs was observed with increasing exposure time, as shown in Table 3. The concentrations of the compounds (Figure 4) exposed to 2 h was 20.38, 90.39, 8.02 and 8.41 for NAP, CRY, BaP and IND, respectively. At 6 h exposure the values decreased to 5.16, 69.44, 3.78 and 4.26 for NAP, CRY, BaP and IND, respectively. By increasing the exposure time the concentration of the pollutants became undetectable, however, the non-detectable range for each pollutant occurred at different hours, i.e., it was 8 h for NAP, 26 h for CRY, 14 h for BaP and 20 h for IND. It is also notable that catalysts, oxidizing agents and UV radiation create free cracks that lead to the removal of pollutants in the soil, as well as the crystalline state of the catalyst.
The UV irradiation alone degraded PAHs and progressed as the exposure was increased. The initial NAP, CRY, BaP and IND were 26.8, 97.7, 9.1 and 9.7 ng/g. NAP concentration becomes non-detectable after 22 h, CRY after 40 h, BaP after 30 h and IND after 40 h of exposure (Table 1); however, when the similar concentrations were exposed to UV irradiation as well as FeCl3/H2O2 (0.3 M FeCl3,10% H2O2), the time taken to degrade PAHs educed significantly. NAP was non-detectable after 10 h of exposure, which depicts that almost the time reduced to half compared to UV exposure alone. A similar trend was observed for CRY, BaP and IND (Table 2). There were further increases in FeCl3/H2O2 (0.4 M, 20% H2O2), and the time taken to degrade PAHs was further reduced. For NAP the concentration becomes non-detectable after 6 h, CRY after 26 h, BaP after 12 h and IND after 18 h (Table 3). These results affirm that the addition of FeCl3/H2O2 produced more electron and electron holes that were responsible for degrading PAH.

3. Discussion

In this study, UV treatment is used to remove carcinogenic PAHCs from industrial soils using an iron-based Fenton reagent. As observed in the study, 60% of NAP was degraded by the 10% iron-based Fenton reagent after 2–10 h of UV exposure. After achieving 99.5% of NAP breakdown (2–6 h UV exposure) iron-based Fenton reagent 20% was used. CRY breakdown under UV exposure (10% iron-based Fenton reagent) was 53% at 2–16 h. At 20% iron-based Fenton reagent CRY breakdown was 82.5–85% at 2–16 h of UV irradiation. BaP at 10% iron-based Fenton reagent gave 57% degradation at 2–10 h whereas 20% reagent gave a 99% degradation rate. For IND degradation was 57% at 10% reagent, which increased to 99% at 20% reagent treatment whereby the exposure time was 2–12 h. The chemical reactions that take place during the procedure can be explained by the following equations [54].
Fe3+ + H2O2 → FeO + H2O
FeO + hυ → e− + h+
e− + O2 → O2−
h+ + H2O → H+ + OH•
Organics + O2−• + OH• → CO2 + H2O + Other degradation
The creation of (OH•) and (O2−) caused degradation of the PAHCs is controlled by the generation of an electron (e−) -hole (h+) pair.
Additionally, the impact of H2O2 on the degradation of NAP, CRY, BaP and IND according to the reaction showed that the more oxidative events where more (OH) free radicals updated rapidly were responsible for PAHCs degradation [55].
H2O2 + hυ → 2OH•
We found that maximum degradation occurred when we applied 30% of the iron catalysts and it was lower in case of 20% iron catalysts. It is because that maximum degradation occurs on the surface of the photocatalysts. The pollutants occupy the active sites of the catalysts, e.g., TiO2 [56], our results are in line with such a statement because the higher the number of active sites, the higher the degradation rate [57]. However there are other factors that might affect the photocatalytic process, as Ziolli and Jardin [56] stated that the complexity of the sample can affect degradation, such as crude oil, which contains a variety of organic compounds, and there exists competition between them for active sites.
Other popular studies like heterogeneous photocatalysis, which uses semiconductors like TiO2, showed a similar phenomenon that helps us to understand the mechanism for pollutant degradation. Semiconductors, e.g., TiO2, contains a forbidden energy region (band gap) between the valance band and conduction band. Electromagnetic radiation, if equal to band gap energy, makes the electron jump from the valance band to the conduction band. The subsequent gap (hole) formed at the valance band tends to oxidize the water adsorbed on the catalysts’ surfaces, forming hydroxyl (OH) radicals, which are highly oxidizing agents, whereas the electron present in the conduction band reacts with oxygen (O2) thus forming reactive oxygen species [58,59,60].
The breakdown of PAHs under hydrogen peroxide alone as well as during the Fenton process (H2O2/Fe2+) shared a common mechanism for breaking down PAHs by forming highly reactive (OH.) radicals. H2O2 alone decomposes to generate OH radicals that break down the PAHs into smaller segments (Figure 5). However, in Fenton processes, more efficient OH radicals are produced: Fe2+ acts as catalyst that reduces H2O2 to produce OH and regenerates Fe2+ in the process.
The iron-based catalyst needs to be effectively separated from soil; this can be achieved via magnetic separation and gravity-assisted settling and centrifugation. After the separation, catalyst physical properties can be restored through physical (heat treatment, air plasma treatment) and chemical (electrochemical regeneration, acid washing and use of reducing agents) regeneration strategies.
The degradation of PAHs is positive and linearly correlated with H2O2 concentration; however, after some optimum results the hydroxyl radicals are transformed to hydroperoxyl radicals, which will lower their oxidation capacity [61,62].
The literature has revealed that oxalic acid at various concentrations was tested and degradation rates for B[a]P increased with the increase in oxalic acid. Li et al. [63] attributed the formation of complexes that separate in the presences of UV radiations to form various radicals and hydrogen peroxide. The OH radicals then facilitate to degradation of B[a]P [64]. The literature further states faster degradation (B[a]P) at lower wavelengths because at a higher wavelength there is less incident radiation energy [65].
Studies state that Fenton treatment requires a large quantity of H2O2 and FeSO4 for the successful removal of pollutants, but in other studies the H2O/Fe2+ ratio is the key to improving Fenton process. It is because optimal H2O2/Fe2+, if maintained, can result in maximal degradation of pollutants because both components can scavenge the radicals generated during the process that will reduce the number of radicals available to the substrate.
The addition of H2O2 acts as electron scavenger that accepts electrons produced in the conduction band of the catalyst. This results in the recombination of electron hole thus leading to an increased concentration of •OH. Under UV radiation the O–O bond breaks down producing more •OH.
Studies have revealed that the reactivity of PAH-bounded residues and ionization potential (IP) and PAH-bound residues are also correlated with H2O2-Fe2+ ratio (m/m) and H2O2 concentrations. Oxalic acid (Chelating agent), in comparison to other acids like citric acid and hydrochloric acid, gave the highest removal percentage (89.5%) of bound PAH residues. Our results are verified with the other studies, like citric acid and oxalic acid along with Fenton application to remove PAHs from contaminated sites [66].
A di-ethylamine (DEA)-related study showed that it was most effective in doses of 1%, which removed 76% of all 12 PAHs. According to research, using DEA boosted PAH clearance from 35% to 76% compared to using merely sun exposure, while increasing the DEA dose had no beneficial effects on PAH remission. At the same optimal dose, the impact of DEA on PAH species is greater for heavy species [67].
Our results shows that PAHs under study were degraded under the influence of UV irradiation alone (Table 1, Figure 2), however the time required to reach the concentration of PAHs to non-detectable levels varied with the type of PAHs. Our results are supported by previous findings that elaborate that photodegradation of PAHs can occur via direct or indirect photolysis [68]; also the photodegradation mainly depends on the properties of PAH and the soil environment [68,69,70]. PAHs absorb photons and shift into single and triplet state acting as initial reactive molecules in direct photolysis, whereas during the indirect process photons are first absorbed by soil components and generate reactive oxygen species that in turn help in PAH degradation.
The absence of a catalyst affirms that a direct photocatalysis took place whereas the addition of a catalyst started indirect photocatalysis of PAHs. We also absorb that after addition of FeCl3, the PAHs photodegradation was accelerated. It is because, after irradiation, catalysts receive energy from the photons and transfer from valence band to conductive band, forming electrons and electron holes [71].
The capacity of hydroxyl radicals to generate super-radical anions (O2−), which accelerates the photolysis of hydrocarbons, can be used to explain this. If no other stress factors are present, temperature control is not required. The chelate solution’s absorbance displayed minimal changes over the course of 9 days without temperature control, indicating good stability of the complexes under aging. The chelate solution initially displayed a short stability when exposed to UV-A radiation, but then gradually exhibited deterioration and released iron. Nevertheless, it was shown that temperature control had the potential to postpone the onset of the instability phenomenon. In actuality, the chelates began to decompose as soon as the solution’s temperature was raised. Nevertheless, due to the release of iron when the temperature was held at 10–15 °C for two hours of irradiation, the complex’s structure was entirely prevented. The evidence that indicates there is no iron release under the entire temperature test range until 45 min after irradiation is quite intriguing [72]. A gradual mineralization of the solution was likewise accomplished under UV-A irradiation (16%). Similarly to this, NPOC removal curves demonstrated a stable first stage, followed by a progressive fall brought on by the impact of the organic radicals created when the chelates broke down. It was impossible to prevent the chelate breakdown and consequent iron release due to the interaction of photochemical and oxidative stressors. As a result, the absorbance reduction curves of the solution indicated a progressive fall since the beginning of the experiment when H2O2 (0.59 mM) was added to the irradiation. Nevertheless, by again adjusting the temperature, it was still possible to extend the lifetime of chelates (from a 60% reduction to a 42% extension in two hours by lowering the temperature by 20 °C). Additionally, the solution’s mineralization began concurrently with the start of the irradiation, much like what was seen with the reduction in chelate content. As a result, the additional oxidation brought on by the creation of hydroxyl radicals only slightly improved NPOC elimination (20%) [73]. The synthesis of catechol, 1-naphthol, salicylic acid and phthalic anhydride as metabolites during the breakdown process is confirmed by GC-MS analysis. The Monod model was used to study the biodegradation kinetics of naphthalene and fluorene, and the maximum rates of degradation were found to be 0.3057 per day for naphthalene and 0.2921 per day for fluorene, respectively [74]. Since delocalized electrons are abundant in PAHs, they can interact strongly with electron-deficient molecules via electron–donor–acceptor interactions great ability of OH to acquire electrons; however, this enables it to aggressively oxidize and destroy PAHs [75]. Because chelated iron is less reactive than free iron, there is evidently less catalysis involved in the breakdown of PS. Moreover, UV-A irradiation cannot guarantee a proper PS activation because it has a considerably lower molar extinction coefficient than UV-C irradiation [76]. The rate and effectiveness of pollution reduction are determined by the intensity of the distributed light [77].
The outcomes showed that the NaP, BaP, CRY and IND degradation were accelerated by the FeCl3 catalyst. Their half-lives were 0.5% shorter. The breakdown rates were likewise affected by the UV wavelengths, demonstrating that the decomposition of PAHCs might vary depending on the UV wavelength used. The findings suggested that the Zn-based Fenton reagent might serve as a substitute for Pyr and Flr degradation in sandy soil, regardless of UV radiation presence. In spite of this, the Zn-based Fenton reagent was marginally more effective than the Fe-based Fenton reagent at photodegrading Pyr and Flr. The rate of PAH degradation was controlled by the formation of radicals of OH and O2− [78].

4. Materials and Methods

4.1. Samples Area

Soil samples under this study were collected from the Industrial Area (Al-Shifah Industrial Area (SHI)) in Riyadh, Saudi Arabia. The soil in the industrial zone is polluted with residues of oils, petroleum materials and repair waste for cars of all kinds. Samples were collected from 0 to 30 cm depth for surface soils.

4.2. Analysis Methods

4.2.1. Photocatalysis Treatment Method and Extraction of PAHCs

The soil collected from the experimental site was homogenized by stirring it with glass rod. The pre-analysis for PAH concentration was carried out on the soil sample. A total of 10 g of soil was placed in glass vials and 35 mL of DCM/PE (1/1) was added, spiked and standard mixed. The samples were placed in an orbital shaker for 5 h (280 rpm) and ultrasonically extracted (for 30 min) and filtered. The extraction process was repeated on the residual sample and then 5 mL of the extract volume was transferred into HEX using a rotary evaporator; 15 mL of HEX was added for the solvent exchange. The methods carried out by Karaca [79] were used for treating the soil samples. The PAHs were analyzed in a gas chromatography chamber. For this, instrument detection limits were determined and calibration was completed. Individual PAHs were identified on the basis of the retention time of target ions peaks. Identification was confirmed by the abundance of the qualifier ion relative to target ion.
The levels of PAHCs in the soil samples taken from the chosen study site were calculated and handled as described [46]. Analogous samples were used. Petri dishes with a 9 cm diameter were filled with 10 g of each type of soil. All Petri dishes in the experiment were exposed to UV radiation at a wavelength of 306 nm [31,80], and the time was recorded every 24 to 42 h every day. The experiment was set up in three duplicates. A precise UV intensity was provided, and the space between bulbs and soil samples was maintained at 12 cm. In order to speed up the effects of ultraviolet light for photo treatment of PAHCs over time, the procedure was also repeated with catalysts (FeCl3) and oxidizing agents (H2O2) present in various ratios of the gas chromatograph quadrant [81].

4.2.2. Determination of PAHCs Using GCMSMS/TQD

Organic substances, such as PAHCs, were found using gas chromatography and a mass spectrometer. For the necessary analysis, ions were identified using a single ion screen (SIM) under standard conditions and a scan mode. To guarantee the accuracy of the duplicated results, titration was carried out for each chemical using samples with various reference concentrations.

4.2.3. Quality Standards for Analysis Methods

To assure the accuracy of the results, the measurement procedures were conducted in accordance with the quality requirements for the compounds under investigation, including the maximum rating (LoQ) should be SN > 10 and linearity (R2) should be equal to or greater than 0.99. All instruments used in the study (whether for digestion, standard solution, or filtration) were cleaned with a 10% HNO3 solution for 24 h while utilizing standard materials and high-purity solvents. They were then dried and repeatedly washed with distilled water to guarantee that they were impurity-free. Additionally, three replicates of each sample from the studied samples will be taken in order to guarantee the accuracy of the reading, and control samples will be taken at every stage of the sample analysis. Additionally, three replicates of each sample from the investigated samples will be taken to guarantee the accuracy of the reading, and control samples will be taken at every stage of the sample analysis.

5. Conclusions

The soils in industrial areas contain a complex mix of pollutants, particularly carcinogenic PAHCs. When treated with ultraviolet rays, there is a noticeable change in the concentration of these compounds. Over time, this treatment alters the compounds’ effectiveness and reduces their toxicity. This results in decreased environmental and health risks for humans and animals over extended periods. When Ferric chloride (FeCl3) with hydrogen peroxide (H2O2) at different percentages, particles are formed, which play a prominent role in cracking the benzene rings of PAHCs. It was found that the application of 0.4 M FeCl3 with 20% H2O2 resulted in an increase in the removal of the studied pollutants compared with 0.3 M FeCl3 with 10% H2O2 has also decontaminated soil but follows a slow process, hence it is recommended to use a high percentage of oxadiazon-catalysis for PAHCs remediation treatment because of high impact removal pollution with PAHCs in a short time. In the future, it is necessary to implement studies related to the regeneration of PAHs, their leaching capacity and how to manage these risks at the field level. Also, there is a dire need to develop catalysts that are compatible with specific pollutants so that maximum remediation is obtained. In future studies, intensity and wavelength-dependent studies will be crucial for fine-tuning the selectivity of appropriate and more effective wavelengths in the photocatalysis process. These studies can include targeting specific excited sites, targeting catalyst designs, competing pathways and optimization of single or multiphoton processes.

Author Contributions

Conceptualization, M.H.E.-S. and A.G.A.; methodology, M.H.E.-S.; software, Z.A.; validation, M.H.E.-S., Z.A. and T.M.A.-B.; formal analysis, M.H.E.-S.; investigation, Z.A.; resources, M.H.E.-S.; data curation, A.G.A.; writing—original draft preparation, M.H.E.-S., Z.A., T.M.A.-B. and A.G.A.; writing—review and editing, M.H.E.-S.; visualization, Z.A.; supervision, M.H.E.-S., Z.A., T.M.A.-B. and A.G.A.; project administration and funding acquisition, M.H.E.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research is part of the ongoing Research Funding Program (ORFFT-2025-074-1), King Saud University, Riyadh, Saudi Arabia.

Data Availability Statement

Data available on request.

Acknowledgments

The authors would like to thank the Ongoing Research Funding Program (ORFFT-2025-074-1), King Saud University, Riyadh, Saudi Arabia, for financial support.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00956 g001
Figure 1. Decomposition of organic compounds by the Fenton process [8].
Figure 1. Decomposition of organic compounds by the Fenton process [8].
Catalysts 15 00956 g001
Catalysts 15 00956 g002
Figure 2. Photo remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm without a catalytic agent.
Figure 2. Photo remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm without a catalytic agent.
Catalysts 15 00956 g002
Catalysts 15 00956 g003
Figure 3. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, with catalysis agent 0.3 M FeCl3 and 10% H2O2.
Figure 3. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, with catalysis agent 0.3 M FeCl3 and 10% H2O2.
Catalysts 15 00956 g003
Catalysts 15 00956 g004
Figure 4. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, with catalysis agent 0.4 M FeCl3 and 20% H2O2.
Figure 4. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, with catalysis agent 0.4 M FeCl3 and 20% H2O2.
Catalysts 15 00956 g004
Catalysts 15 00956 g005
Figure 5. Heterogenous photocatalysis procedure.
Figure 5. Heterogenous photocatalysis procedure.
Catalysts 15 00956 g005
Table 1. Photo remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using 306 nm Control.
Table 1. Photo remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using 306 nm Control.
Time (h)PAHCs (ng/g)
NAPCRYBaPIND
026.8 ± 1.8797.7 ± 0.79.1 ± 0.79.7 ± 0.4
224.66 ± 2.0895.11 ± 2.038.91 ± 0.429.06 ± 0.34
323.02 ± 3.5691.34 ± 2.158.03 ± 0.518.78 ± 1.58
421.37 ± 3.2287.44 ± 1.467.25 ± 1.338.35 ± 1.17
619.68 ± 1.4482.41 ± 1.466.39 ± 1.227.66 ± 1.02
817.23 ± 1.7178.11 ± 1.066.01 ± 1.047.04 ± 1.22
1015.66 ± 1.1674.12 ± 2.195.24 ± 1.126.38 ± 1.06
1213.63 ± 1.2371.88 ± 2.714.41 ± 1.786.02 ± 1.14
1410.55 ± 1.4368.33 ± 2.274.13 ± 0.625.55 ± 0.72
168.12 ± 0.8264.57 ± 2.013.61 ± 0.445.17 ± 0.23
185.03 ± 0.5759.22 ± 2.463.04 ± 0.324.39 ± 0.61
202.17 ± 0.3654.46 ± 1.232.27 ± 0.413.77 ± 0.81
22Not detected 48.22 ± 1.162.02 ± 0.613.27 ± 0.31
24Not detected 43.57 ± 0.811.48 ± 0.273.06 ± 0.56
26Not detected 39.23 ± 2.261.21 ± 0.372.81 ± 0.71
28Not detected 33.66 ± 2.390.83 ± 0.172.35 ± 0.44
30Not detected 28.11 ± 2.280.33 ± 0.112.02 ± 0.22
32Not detected 21.33 ± 2.03Not detected1.64 ± 0.45
34Not detected 16.78 ± 1.35Not detected1.29 ± 0.33
36Not detected 11.28 ± 1.17Not detected1.11 ± 0.22
38Not detected 7.66 ± 1.34Not detected0.71 ± 0.28
40Not detected 3.14 ± 0.22Not detected0.46 ± 0.11
42Not detected Not detectedNot detectedNot detected
Table 2. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, FeCl3 and H2O2 the 0.3 M FeCl3 with 10% H2O2.
Table 2. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, FeCl3 and H2O2 the 0.3 M FeCl3 with 10% H2O2.
Time (h)PAHCs (ng/g)
NAPCRYBaPIND
026.8 ± 1.8797.7 ± 0.79.1 ± 0.79.7 ± 0.4
222.11 ± 1.2693.55 ± 3.398.69 ± 1.119.04 ± 0.75
319.51 ± 1.0389.22 ± 3.097.28 ± 0.778.11 ± 0.49
416.29 ± 0.8985.37 ± 3.276.39 ± 0.577.02 ± 0.41
611.44 ± 1.3781.88 ± 1.665.22 ± 0.616.17 ± 0.36
87.78 ± 1.7175.60 ± 1.894.18 ± 0.455.01 ± 0.19
104.66 ± 1.0270.19 ± 2.523.66 ± 0.334.07 ± 0.42
12Not detected 64.77 ± 2.922.71 ± 0.293.22 ± 0.61
14Not detected 57.08 ± 1.711.84 ± 0.262.51 ± 0.26
16Not detected 48.66 ± 2.381.27 ± 0.212.17 ± 0.31
18Not detected 39.11 ± 2.040.73 ± 0.061.73 ± 0.42
20Not detected 30.28 ± 1.330.23 ± 0.111.02 ± 0.16
22Not detected 23.79 ± 1.88Not detected 0.61 ± 0.09
24Not detected 16.33 ± 2.04Not detected 0.37 ± 0.06
26Not detected 10.29 ± 1.44Not detected Not detected
28Not detected 7.46 ± 1.37Not detected Not detected
30Not detected 2.41 ± 1.03Not detected Not detected
32Not detected Not detected Not detected Not detected
Table 3. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, FeCl3 and H2O2 0.4 M FeCl3 with 20% H2O2.
Table 3. Photocatalysis remediation impact treatment on mean concentrations of PAHCs compounds in (SHI) industrial soils (Oils pollution) using wavelength 306 nm, FeCl3 and H2O2 0.4 M FeCl3 with 20% H2O2.
Time (h)PAHCs
NAPCRYBaPIND
026.8 ± 1.8797.7 ± 0.79.1 ± 0.79.7 ± 0.4
220.38 ± 0.7890.39 ± 2.068.02 ± 1.248.41 ± 1.51
314.45 ± 1.1983.77 ± 2.596.11 ± 0.697.21 ± 0.66
411.27 ± 0.9375.66 ± 2.685.15 ± 0.725.77 ± 0.49
65.16 ± 0.8269.44 ± 1.553.78 ± 0.444.26 ± 0.78
8Not detected 61.18 ± 1.212.27 ± 0.673.66 ± 0.48
10Not detected 54.77 ± 2.361.44 ± 0.573.02 ± 0.17
12Not detected 45.08 ± 2.110.71 ± 0.232.18 ± 0.15
14Not detected 37.23 ± 1.58Not detected 1.45 ± 0.28
16Not detected 26.34 ± 2.17Not detected 1.04 ± 0.19
18Not detected 19.18 ± 0.84Not detected 0.65 ± 0.12
20Not detected 12.56 ± 1.12Not detected Not detected
22Not detected 8.99 ± 1.04Not detected Not detected
24Not detected 4.05 ± 0.68Not detected Not detected
26Not detected Not detected Not detected Not detected
28Not detected Not detected Not detected Not detected
30Not detected Not detected Not detected Not detected
32Not detected Not detected Not detected Not detected
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EL-Saeid, M.H.; Alghamdi, A.G.; Alasmary, Z.; Al-Bugami, T.M. Photocatalytic Remediation of Carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs) Using UV/FeCl3 in Industrial Soil. Catalysts 2025, 15, 956. https://doi.org/10.3390/catal15100956

AMA Style

EL-Saeid MH, Alghamdi AG, Alasmary Z, Al-Bugami TM. Photocatalytic Remediation of Carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs) Using UV/FeCl3 in Industrial Soil. Catalysts. 2025; 15(10):956. https://doi.org/10.3390/catal15100956

Chicago/Turabian Style

EL-Saeid, Mohamed Hamza, Abdulaziz G. Alghamdi, Zafer Alasmary, and Thawab M. Al-Bugami. 2025. "Photocatalytic Remediation of Carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs) Using UV/FeCl3 in Industrial Soil" Catalysts 15, no. 10: 956. https://doi.org/10.3390/catal15100956

APA Style

EL-Saeid, M. H., Alghamdi, A. G., Alasmary, Z., & Al-Bugami, T. M. (2025). Photocatalytic Remediation of Carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs) Using UV/FeCl3 in Industrial Soil. Catalysts, 15(10), 956. https://doi.org/10.3390/catal15100956

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